A plant as described above is conventionally used for the production of commercial solutions of hydrogen peroxide. An example of such a plant is presented in the work by Kirk Othmer, "Encyclopedia of Chemical Technology", 3rd edition, volume 17.
For economic reasons (cf. Process Economic Report No. 68B, Hydrogen Peroxide, March 1992, chapter VI, SRI international) which are essentially linked with the costs of transportation and storage, these solutions must have a hydrogen peroxide concentration that is as high as possible, that is a concentration higher than 35%, more generally a concentration of 60% or 70% by weight.
To prepare these concentrated commercial hydrogen peroxide solutions, the process is run so as to recover at the outlet of the extractor a solution which has a hydrogen peroxide concentration that is as high as possible, while remaining outside the region of explosiveness of the mixtures of working solutions/aqueous solutions of hydrogen peroxide. In this respect, Patent Application FR-A-2,228,717 points out that the hydrogen peroxide concentration of said aqueous solution leaving the extractor must not be higher than 600 g/l, that is 50% by weight of hydrogen peroxide. A hydrogen peroxide concentration higher than this value is described as being capable of producing explosive reactions.
To obtain highly concentrated aqueous solutions of hydrogen peroxide, the operating parameters of the above-mentioned autooxidation plant are adapted so as to permit the use of a working solution which has, throughout the plant, a hydrogen peroxide equivalent which is as high as possible, for example a hydrogen peroxide equivalent higher than 11 g/l, or even higher. Thus, Patent Application FR-A-2,086,166 recommends the use of a working solution capable of producing, after oxidation, a quantity of the order of 16 g of hydrogen peroxide per liter of working solution. The hydrogen peroxide equivalent is thus at least 16 g/l at the entry of the oxidizer. However, conventional plants using a high hydrogen peroxide equivalent present numerous disadvantages. Thus, they generally require the use of high oxidation temperatures. These temperatures become necessary to prevent the crystallization of the working solution which has a high hydrogen peroxide equivalent. In this respect reference may be made to "Techniques de l'Ingenieur", chapter "Peroxyde d'hydrogene", J. 6020, which mentions that the oxidation temperatures must be between 60 and 80.degree. C.
Another disadvantage encountered in these plants is that the working solution decomposes rapidly.
In addition, these traditional plants are very sensitive to the presence of water, even in a small quantity, which can be introduced accidentally either into the oxidizer or into the conduits linking the oxidizer and the extractor. In this region the water reacts with the oxidized working solution, which can give rise to explosive reactions.
In addition, in order to reduce the risk of explosion in the oxidizer, it is necessary to employ "dumped" random packings (for example Raschig rings). These packings have good characteristics insofar as the gas-liquid contacts are concerned, but they are costly to use and take up a lot of room in the oxidizer. Furthermore, these packings have a tendency to retain solid impurities. Thus, when being started up again, the plant is exposed to a high risk of a relatively large quantity of impurities, especially metallic ones, suddenly entering the extractor, and this is dangerous in this part of the plant.
The objective of the present invention is to circumvent the abovementioned disadvantages.
More particularly, the objective of the invention is to provide a plant for the production of hydrogen peroxide using the autooxidation technique, which is particularly well suited from the viewpoint of capital cost, operating costs and safety in the actual industrial conditions. In particular, the objective of the invention is to provide a plant that enables hydrogen peroxide to be produced directly on the site where it is used by certain plants, such as plants for the manufacture of paper pulp.